How does it go in play mode ? are you running out of memory or feeling the performance drops ?
You can get away with a fair amount of modular pieces with world streaming on, anything outside the props loading range will be HLOD generated meshes of your buildings.
If your performance is struggling on 8192 for the cell size and loading range, then it may be something to worry about.
I did note you have Z -8.319 on your building. I have noticed that when using modular pieces there is a slight memory increase for using any angles other than 0,90,180,-90.
I have a bunch of props… prop circles, hexagon, octogon, dodeca builds and it chews up memory a fair amount more than the same amount of power 2 grid aligned props.